A basic norm of international law—embedded in the international order for several decades—prohibits a state from forcibly taking foreign territory. But conflicts over territory are becoming more common, says Monica Hakimi, William S. Beinecke Professor of Law. Her research, with Professor Ingrid Brunk at Vanderbilt Law School, suggests that the spread of territorial conflict could have catastrophic consequences in a world in which U.S. geopolitical influence is under pressure.

What does international law say about one state attempting to take territory from another?  

International law provides that territorial disputes must be resolved amicably and at the international level. The International Court of Justice has been instrumental in helping states resolve territorial and, by association, maritime disputes over the years—including in cases between Malaysia and Singapore, Nicaragua and a number of its neighbors, Peru and Chile, Romania and Ukraine, Benin and Niger, and Qatar and Bahrain. Nevertheless, many territorial and maritime borders remain contested, and even borders that were once largely taken to be settled can be reopened by those who hold historic grievances, raising the potential for future conflict.

The prohibition of annexations helps to “lock” settled borders in place by providing that states may not acquire territory through the threat or use of force. This prohibition did not always exist and was extraordinarily difficult to codify. Though many scholars trace it back to the United Nations Charter, which states adopted at the end of World War II, it was solidified as an absolute prohibition—permitting no exception, even for lawful uses of force—through the massive wave of decolonization of the 1950s and 1960s.

Where are some of the territorial disputes occurring now, and why is this kind of conflict so worrisome?

The conflicts between Russia and Ukraine, Israel and Hamas in Gaza, Azerbaijan and Armenia, Venezuela and Guyana, Ethiopia and Somalia, and China and several of its neighbors are all territorial conflicts: They go to the question of who has sovereign title to—and with it, the right to control—the territories at issue. Those conflicts have also all escalated in recent years. 

Historically, territorial conflicts have tended to be the most intense conflicts and the hardest to resolve. They are more likely than other kinds of interstate disputes to become militarized, and, once they are militarized, also more likely to be more deadly and to spiral into regional or global wars. The two World Wars and the experiences of European colonialism in Africa and elsewhere were all territorial conflicts and brought immense human suffering.

Fighting over territory is not a new phenomenon, as you point out. Why is it of special concern now? 

The international order is undergoing a period of dramatic change. International lawyers and political scientists have spent considerable time analyzing where we are heading because the changes are so destabilizing. But they have not, in my and Professor Brunk’s view, focused enough attention on the factors that are contributing to a rise in territorial conflicts. Our concern is that, as the prohibition of annexations became deeply entrenched in international law, its significance also faded from view. Thus, rather than being seen as a distinct norm, it is often folded into other norms with which it is intertwined. However, the prohibition of annexations is not the same as, and should not be conflated with, any other international legal norm. It is foundational precisely because it undergirds and ties together three separate normative projects in international law: one that entrenches state authority in defined territorial spaces, a second that fosters peace among territorially defined states, and a third that provides for the self-determination of peoples within such states.

Even now, as the world has witnessed a reignition of territorial conflicts, most analysts have not analyzed these conflicts together as being specifically about territory and thus have overlooked that this norm is at stake. As a result, this prohibition is at risk of slipping away, if for no reason other than that not enough actors are doing enough to insist that, on whatever else they might disagree, it should remain inviolable. 

How has the United States played a role in upholding the prohibition of annexations?

Since the end of World War II, U.S. military power has been critical to forestalling territorial conflicts around the world. To be sure, the United States has also used its military power in a broad range of conflicts, from Afghanistan to Kosovo, Iraq, Libya, and beyond, often with devastating consequences. But the United States did not annex territory in any of those operations. Instead, it has, through its security guarantees, protected the territories of dozens of other countries in Europe, the Americas, Asia, and the Middle East—countries that would have been more vulnerable without the heft of a superpower behind them. It has taken discrete actions to preserve the territories of states not under its security umbrella, such as Kuwait in 1990 to 1991 and, more recently, Ukraine. So, while U.S. military power has undoubtedly imposed real costs on the world, it has also helped secure what has been the foundational norm of international law during this period. 

How is that changing? 

The international response to territorial annexation has gotten caught up in a broader contest over the future of the world—and specifically over the U.S. position of dominance. China, like Russia, is seeking to change the international order in which the United States has been dominant. Its support for the prohibition of annexations has taken a back seat to its broader geopolitical contest with the United States. The majority of states have also responded to Russia’s open assault on this norm with a compromised message: that however problematic Russia’s conduct might have been, it was not worth the effort that would be required to uphold the norm, given everything else in play.

Meanwhile, it has become increasingly clear that the United States is either unable or unwilling to do what is necessary to protect, at the same time, all of the territories under its protection that are now vulnerable to attack. U.S. domestic politics have only heightened the uncertainty about what the United States would do in the face of further efforts to forcibly seize territory from one or more of its security allies or from another state. The growing sense that the United States would not, should not—or even could not—step in to protect the territorial status quo puts the prohibition at systemic risk, as others jockey for an upper hand.

What do you see as the future of the annexation prohibition?

The question that the world now confronts is whether a new set of social forces can and should emerge to sustain the prohibition on annexation and limit conflicts over territory. There are not currently any plausible proposals for replacing states, defined by territory, as the main units for political organization in the world. So the erosion of the prohibition of annexations—and with it, the broader set of norms that protect states’ territorial borders from forcible change—threatens to have negative, long-lasting consequences for many of the same peoples that such proposals are designed to protect. Absent a new global politics that commits to upholding this norm, I fear that territorial conflicts of the sort that are unfolding in Ukraine and Gaza will become more common and run the risk of metastasizing into a full-blown war among the most powerful—and most heavily nuclear-armed—states on earth. 

This interview has been edited and condensed.